So you want to know about Down and Synthetic and what bag you should choose? The answer may not be easy. There are a few variables that mean one bag may be better than the other – sometimes.
Here is a quick comparison of some of the highlights of the two fills.
Down
Lightweight, Easy to compress and Resilient
Synthetic
Quick-drying, Insulates when wet, Non-allergenic and usually Cheaper
Lets start with the “fill” and what it means and how it helps you.The “Fill” is the standard used to measure down’s ability to loft. It is represented by how many cubic inches 1 ounce of down can fill in a standardized testing device, the fluffier and fuller the down the better the numbers. Therefor a higher fill number will result in a lighter bag. For example it takes less 700 fill down to fill the same 30 degree rated bag as it would for 500 fill down. This will result in a lighter weight bag – even if it is a slight amount of weight every ounce counts sometimes.
Down is a fantastic insulator. It works best in dry conditions and compresses better than synthetics and weighs less than a comparable synthetic bag. There are a few trade off though –down is expensive but it maintains its loft much longer than synthetics. Some people are allergic to down so it may not even be an option. Down is also not a fan of water and when saturated will lose its insulation properties unlike synthetic fill bags so in wetter areas or places where you may experience rain it may not be the best choice.
When down becomes saturated it loses nearly all of its insulating properties. Newer bags do have hydrophobic chemicals added that will bind to the down and help to repel water. Although the result is not waterproof, it is water resistant. Since the treated down has hit the market there have been tests done that shows that the water-resistant down may dry out faster than non-treated down. But this all goes out the window during a downpour or if you fall in a stream or lake.
Another option to protect the down is to buy a dry sack to keep the bag in until you have your tent setup. This will keep it dry in a downpour or if you have an accident near water. It also protects you from a camelbak leak if you manage to pop a bladder. The dry sack should only be used for when you are backpacking – you should not store your down bag in it when your home.
Down should be stored in an area where it can breath. When you get home from a trip you should fully air out your bag and make sure it is completely dry. Most down sleeping bags will come with a storage bag. Its usually about the size of a laundry bag and is ventilated. I just hang mine in the back of my closet and every now and then when I am putting clothes away I give it a whack to fluff it. You should not store it in its stuff sack.
Down is very resilient, capable of being repeatedly shoved in a stuff sack without compromising its ability to insulate. It is also extremely compressible, and this is where it edges out synthetic insulation and saves you a ton of space. Here is a photo of a Marmot 30 degree down bag semi compressed. And it will compress further when in the pack.
Now for the Synthetic Insulation.
Synthetic insulation is for the most part less expensive than a comparable down bag and it dries much faster. Another plus is that synthetics are nonallergenic so they may be the best or only choice for some people who are allergic to down.
A synthetic bag will give the user less in the warmth to weight ratio as it takes more synthetic fill to achieve the same temp rating as down. Synthetics will also be a bit bulkier when packed down and some synthetics tend to break down and lose the ability to insulate faster than a high quality down bag will. Both will eventually need replacing though. However you can store synthetics in their stuff sack, so if your in a space restricted home or apartment it may be a bonus for you.
For compressibility down wins over synthetic hands down, but where synthetics shine is the ability to maintain warmth when wet. That makes it a good choice for some backpacking situations as synthetic insulation is much better at keeping the user somewhat comfortable even if they are soaked. Common sense tells you to keep your sleeping bag dry as possible, but accidents and unforeseen weather happen. For rainier climates or river trips I always reach for synthetics as a “just in case” precaution. I have been stuck in a storm with a synthetic zero degree bag and slept fine even as the snow fell on top of me. It was definitely wet in the morning (not soaked) but I was still warm.
So there you have it, what both fills can do and not do and where one will shine but another fail. It leaves you to decide what is best for your trip. Or if maybe you should splurge and buy one of each and cover all your bases.
Happy sleeping
